1. Field of the Invention
The present invention relates to an information storage system employing a novel optical-based information storage media having multiple information storage layers each of which have a characteristic wavelength and polarization state, and from which recorded information can be read by a laser beam having similar wavelength and polarization-state characteristics in order to provide a significant improvement in information storage capacity.
2. Brief Description of Prior Art
In the contemporary period, there is a great need for high density information storage media. For decades, magnetic disc and tape have been the dominant information storage media for recording both analog and digital information. In more recent times, the trend has changed to optical storage media because of its higher information storage capacity. In principle, each optical storage media exploits one or more characteristics of light and its interaction with matter in order to store and access information.
In conventional optical CD-ROM technology, digital information in the form of a logical "0" is recorded as a microscopic protrusion formed on the reflective surface of the compact disc along a continuous spiral track, whereas a logical "1" is recorded as a microscopic section of planar surface area the size of about the cross-sectional diameter of the focused laser beam used during information reading operations. When an incident laser beam is reflected off such microscopic protrusions during information reading operations, a reduction in intensity of the reflected laser beam is detected by the photodetector of the CD-ROM drive unit and is converted into a logical signal. In conventional CD-ROM technology, the primary limitation on information storage capacity is determined by protrusion size. Consequently, great efforts are being undertaken to make inexpensive laser diodes that produce laser beams with shorter wavelengths for use in detecting smaller-sized protrusions during information reading operations.
Recently, there have been attempts to increase the information storage capacity of conventional CD-ROM devices. One technique in particular, which has received popular attention, is disclosed in U.S. Pat. No. 5,381,401. In essence, this technique involves stacking up multiple information layers of optically, substantially transmissive material, each realized by an regular CD disc having a thin aluminum film coating with a light reflectance of about 4%. By adjusting the depth of focus of the laser beam used during information reading operations, it is possible to read information from a selected information storage disc. However, a major drawback with this prior art technique is that only a relatively small number of information layers can be stacked up before severe attenuation of the reflected laser beam occurs, thereby resulting in an unacceptable signal-to-noise ratio and thus system performance.
An altogether different approach to optical mass storage has been taught in recently issued U.S. Pat. No. 5,353,247 to Faris, co-applicant of the present application. Rather than using semi-reflective coatings, as taught in U.S. Pat. No. 5,381,401, U.S. Pat. No. 5,353,247 teaches the use of the wavelength-selective property of the Cholesteric Liquid Crystal (CLC) material, and discloses an optical storage media comprising multiple information storage layers made of CLC material. However, a major drawback with this prior art system is that N laser lines (i.e. spectral components) are required to read N number of CLC-based information storage layers. How this shortcoming might be overcome is neither disclosed, taught or suggested by the prior art.
Thus there presently is a great need in the art for an improved method and apparatus for storing and retrieving information in a manner which achieves a substantial improvement in information storage capacity over prior art systems and methodologies.